Start with a light pencil (2H), and start drawing the facial features very lightly.
I recommend drawing the eyes, nose, and then mouth, in that order, but that is not to say you cannot start with the mouth
and work your way up.
Whatever feels comfortable to you.

Step 3 =

Once the face is drawn, start going a little darker so the face starts to come to life.
Remember to keep looking at the ref and your drawing, and make the necessary adjustments.

The most important RULE I leanrt is:

Just draw what you see.

Step 4 =

Once you're happy with the face, start drawing the hair.
Remember the hair can be pretty difficult, but just keep at it.